78 KZ650 - No Power

This is my 78 kz650. As you can see it has been turned into a hardtail with pods and the exhaust has been split 2:1 on each side of the bike. The carbs have been cleaned and the main jet changed to a 105 and the needles to full rich.

No problem starting or idling. Pulls great in 1,2 and 3 with slight hesitation at higher rpm.

Now when I test drove the bike I could not get it above 95 km/h and there was hesitation and some backfiring at that speed (mostly in 4th and 5th). Also, there is deceleration backfiring that occurs at higher speeds.

Any suggestions on how I can get this thing running right? I don't need to set land speed records but I need to get up to highway speeds.

59mph only?

Before jumping into carbs...

All other variables in spec?
i.e. compression, leak down test, valve to shim clearances, ignition timing, carbs synced, power to coils etc....

Prior to carb and exhaust changes, did you have this issue?

Outside of the above mentioned, assuming in spec, first thing that jumps out is too lean on the needle/needle clip position thus "Falling on it's Face" in power... Since you mentioned it's at the richest position, change to richer needle.

Possibly Main jet still too lean as well....

Question, what condition are the spark plugs?
If hot white then too lean still....
Pre detonations?
Banding strap mark where?

Maybe this will help....
kzrider.com/index.php?option=com_docman&...d&gid=461&Itemid=108

OMR